Technical Field
This application generally relates to fuel cells, and more particularly, the application relates to managing gases within a fuel cell.
Description of the Related Art
A fuel cell uses a cathode and anode that receive oxidant, such as air, and fuel, such as hydrogen, respectively, to generate an electrochemical reaction that produces electricity, as is well known. Typically, the cathode and anode are separated by a solid separator plate which prevents commingling of reactant gases but provides for electrical conductivity. The fuel cell typically includes numerous cells that form a stack. The cells may include water transport plates, which are porous separator plates through which water passes, but not appreciable quantities of gas. The water transport plate is hydrated by a water flow field on one side, the water flowing through the plate to humidify the reactant stream (fuel or oxidant) on the other side. The humidified reactant stream permits membrane hydration, which is important to successful operation of the fuel cell. The water transport plate also enables removal of product water which is generated on the cathode by the electrochemical reaction. In some example fuel cells, the circulated water acts as a coolant.
The volume of water within the stack must be managed to maintain a desired amount of water, for example, for membrane hydration, cell cooling, and minimizing the effects of sub-freezing environments. In one type of cooling system, water is evaporated into a cathode reactant flow field and then condensed in an external device to return liquid water to the fuel cell's water flow field. Systems employing evaporatively cooled fuel cells have far less water than similar fuel cells using other types of cooling strategies. However, gases may become entrained in the coolant passages due to leakage from ambient surroundings, or reactant crossover through the seals or the pores of the water transport plates, on the order of one cubic centimeter per minute per cell in the stack in one example. Entrained gases inhibit the replenishment of liquid water to the water flow field, which can cause operational problems with the fuel cell. The gases must be expelled from the fuel cell to maintain desired operation of the fuel cell.
What is needed is a method and apparatus of releasing gases from the coolant passages of the fuel cell.